“Marriage gives that fulness to life which nothing else can give,” said Helmholtz when I saw him again in Berlin and informed him that I was married and that I had been promised an academic position at Columbia College. He approved my dropping the experimental research and substituting in its place a mathematical research in physical chemistry. This research was finished in the early spring and I sent it to Helmholtz who was then in Baden-Baden. He telegraphed: “Your successful effort approved and accepted.” Never before nor since did I ever receive a telegram which made me more happy. The examinations gave me no serious trouble, and in the late spring of that year I had my doctor’s degree and became a citizen in the world of science. The three theses which, according to old German custom, every candidate seeking promotion to the dignity of a doctor of philosophy must frame and defend publicly are given here, in order to show my final mental attitude which was formulated by my scientific studies in Europe. I. Instruction in Physics in the preparatory schools should be as much as possible a practical one. II. The Thermodynamic methods of Gibbs, von Helmholtz, and Planck form the most reliable foundation for the study of those physical processes which we cannot analyze by ordinary dynamics. III. The Electromagnetic Theory of Light deserves more attention than it has received so far in university lectures. Usually these theses, appended to German doctor dissertations, are not taken very seriously either by the candidate, who is to be promoted, or by anybody else. But I took my theses very seriously. The first summed up President Barnard’s doctrine relating to scientific instruction, which I described before in connection with my description of the American movement favoring scientific research in American colleges and universities; the second summed up my admiration for the new science of physical chemistry first started by our own Josiah Willard Gibbs; and the third summed up my love for the Faraday-Maxwell electromagnetic science. On these three questions in physical science I had, I thought, quite clear and definite ideas; and that gave me much confidence that I was about to return to the United States sufficiently equipped to render service in return for some of the many favors which I had received.